This invention relates generally to a controller of the type suitable for use with an electrical motor. More specifically, this invention relates to a motor controller which receives at least one operating signal from a microprocessor-based system. Preferably, the microprocessor-based system includes a linear program for generating the operating signal. The program operates in synchrony with a recurring signal provided to the reset terminal of the microprocessor.
In a preferred embodiment, the invention also relates to a motor controller operatively connected to a microprocessor-based system for use in recreational vehicle ("RV") heating systems. The motor controller is described herein with reference to a combustible fuel burner system, however, the invention is not so limited. The invention is in fact applicable in any application where the control of a motor is desired.
A combustible fuel burner system such as those employed in RV heating systems generally includes an ignition system and a blower. The ignition system typically includes an output relay for energizing a gas valve, a spark generator for igniting the gas available at the gas valve, and a flame-sensing probe for detecting the presence of a flame. The ignition system generally operates to control a flame associated with the heating system.
The flame is typically located in a combustion chamber. The flame heats air in a heat exchanger. The blower forces the heated air out of the heat exchanger and into an RV living space. The blowers or fans associated with RV heating systems generally include a direct current (DC) motor. The motor in such prior art systems is generally controlled by a relay which provides DC power to the motor. Such prior art DC motors are generally powered by a full wave rectified supply created by voltage converters used at most RV parks or by a 12 volt DC battery.
An example of a microprocessor-based controller is disclosed in U.S. Pat. No. 4,581,697 entitled "Controller for Combustible Fuel Burner," issued to Jamieson et al. on Apr. 8, 1986. In U.S. Pat. No. 4,581,697, the microprocessor-based apparatus controls the operation of a combustible fuel burner. The apparatus utilizes a synchronizing signal for monitoring the integrity of certain circuit components, which may incorporate one or more input and output stages. The apparatus is adaptable to conduct control sequences in accordance with predetermined lapses of time rather than upon the occurrence of predetermined events.
A microprocessor-based control system offering a high degree of reliability and readily adaptable to a wide variety of control strategies is described and shown in U.S. Pat. No. 4,931,975 entitled "Microprocessor-Based Controller with Synchronous Reset," issued to Gleason et al. on June 25, 1990, and U.S. Pat. No. 5,051,936 entitled "Microprocessor-Based Controller with Synchronous Reset, " issued to Gleason et al on Sep. 24, 1991. Such a prior art microprocessor-based system executes a linear program to provide output signals which reliably control the operation of a combustible fuel furnace. Reset signals are applied to the reset terminal of a microprocessor in the system for causing the microprocessor to enter active and inactive states. To ensure operational reliability, the microprocessor includes means for performing a plurality of data integrity checks upon entering the active state and further includes means for calculating and storing information prior to entering the inactive state.
Although the microprocessor-based control system in U.S. Pat. Nos. 4,931,975 and 5,051,936 ensures the operational reliability of the ignition system, no such system has been employed including a circuit to also reliably and accurately control the electric motor associated with the blower. Heretofore, prior art controllers in RV heating systems have not precisely controlled the speed of the motor over various operating voltages. The speed of the motor affects the amount of air moved by the fan or blower. Motor speed is affected by the amount of power supplied to the DC motor. If the voltage supplied to a DC motor is increased, generally the DC motor speed increases. Small increases in voltages generally result in large increases in speed and consequently, significant increases in the volume of air moved by the blower. In RV gas-fired heating systems, the performance of the heating operation is greatly affected by small changes in voltage.
Recent industry trends towards decreasing the size of RV heating systems require the use of small DC motors. Small DC motors are particularly susceptible to variations in motor speed due to variations in supply voltage. The variation in air flow rate due to variation in motor speed has made the design of efficient heat exchangers difficult.
The voltage received by RV heating systems varies from the virtually pure DC of a battery to the full wave rectified sign-wave voltage supplied by the voltage converters used at most RV parks. Additionally, a large variation in supply voltage occurs over the charge/discharge cycle of RV batteries. For instance, a fully charged RV battery supplies approximately 15 volts DC to the motor, and an almost fully discharged battery supplies approximately 9 volts DC. This 6 volt DC variation creates a large variation in motor speed. Thus, the large variation in supply voltage over the charge/discharge cycle of the battery creates a large variation in air flow through the heat exchanger. Also, a large variation may occur in the effective line voltage created by the voltage converters employed at the RV parks. The variation in line voltage results in a large variation in motor speed which consequently creates a large variation in air flow through the heat exchanger. Such large fluctuations in air flow result in occupant discomfort, poor heating and energy efficiency, and noise nuisances.
Heretofore, RV blowers generally employed a motor controller generally utilizing only a relay switch for starting and stopping the motor without circuitry for controlling the motor speed. Such prior art design schemes for a motor controller are susceptible to changes in supply voltages. Further, the control of the DC motor used in an RV heating system requires a highly reliable and readily adaptable motor controller. In an RV heating system and in other applications requiring a high degree of reliability, it is necessary to be able to predict or limit the possible failure modes of the system. While a high degree of reliability can be accomplished in ignition systems, heretofore this has not been done with motor controller systems. Accordingly, the integration of a full motor controller into a standard microprocessor-based ignition system is a significant advance in the art. Thus, a motor controller for use with an ignition system similar to the systems disclosed in U.S. Pat. Nos. 4,931,975 and 5,051,936 provides a highly reliable readily adaptable motor controller which is not disadvantageously susceptible to variations in the supply voltage.